1. Field of the Invention
The present invention relates to an automatic control system for position following and reciprocate motion of a controlled object.
2. Brief Description of the Prior Art
Before going into the description of the detailed background of the present invention, a feedback automatic control system is illustrated hereinbelow with reference to the block diagram of FIG. 1. FIG. 1 shows a block diagram of a feedback automatic control system wherein the numeral 01 represents the system controlled, 02 is a detecting means, 03 is the signal converting means, 04 is the comparing means and 05 is the controlling means. In this system, the controlled variable in the form of electric current is detected by the detecting means 02 from the system controlled 01. The controlled variable is converted into a certain related physical quantity by the signal converting means 03 and fed into the comparing means 04. The deviation value generated by the comparing means 04 is fed into the controlling means 05 as the manipulated variable for automatically controlling the system controlled 01 preserving at a presetted desired value.
It is easily understood that a controlled object to follow a demanding signal to move to a presetted position is usually necessary. For example, a high speed moving train must be decelerated before it comes to a stop for preventing the shock of the same and also to have an accurate stopping position.
Same requirements apply to the controlled object in a working machine. No matter the controlled object is to move to left or right, up or down, forward or backward, it always have a stopping position. And the controlled object must be started to decelerate before approaching the stopping position. Therefore, the conventional positioning mechanism in which the tool of drill will be automatically stopped at a presetted position comprises a high speed motor and a low speed motor. Referring to FIG. 2 which is an illustrative diagram of the relation between position and speed of a controlled object, point A is the presetted stopping position, B is a point before A. The controlled object moves with a high speed in a first period of distance a. Passing point B, a micro switch which is located at B is actuated to stop the high speed motor and the low speed motor begins to move to substitute the high speed motor. The controlled object decelerates in the second period of distance b and keeps a low speed y in the third period of distance c. When the controlled object arrives position A, another micro switch which is located at A is actuated to start a brake means and to stop the low speed motor and thus the controlled object comes to a stop at point C.
In view of the above description, because of the inertia, the controlled object always move beyond the presetted stopping position i.e. stops at point C rather than A, over shoot AC can not be avoid although the brake means is used. Besides, in said conventional positioning mechanism, a plurality of micro switches must be equipped in the mechanism. This will cause the complexity of the system. If the stopping position is to be changed, all the said microswitches must be detached and rearranged at a certain new position. This new rearrangement operation usually complicate and time consuming, and the system will be easily damaged. And this is the main disadvantage of a conventional working machine.
Hydraulic working machines have been well improved and employed by the factories in the recent days. Although there are many advantages for the hydraulic machines but the controlled object is moved with constant speed, the over shoot AC as stated in FIG. 2 still exists. Still it is necessary to equip with the system a micro switch at the desired stopping point. And the difficulty in rearranging the micro switches still exists. Some hydraulic machines use deceleration valves to achieve the deceleration. However this kind of machines must have a related dog for cooperating with the deceleration valve. If the dog is not precisely designed, the best deceleration for the controlled object can still not be obtained.
No matter to use micro switches or the deceleration valves which are usually presetted at the presetted point by a screw or other, if the stopping position is to be changed, the procedure for rearranging these micro switches or valves is much complicated and time consuming. Besides, due to the complexity of the oil passages for a working machine having deceleration valve, it always occupy a huge space and inconveniently operated. As the deceleration valve should be operated mannally, it is impossible to be remote controlled or automatically controlled.
Recently, hydraulic servo mechanism the controlled object will follow the demanding signal quickly, such as servo valve has been developed for ships and airplanes to control the aviation direction in turn of the driving wheel operated by the pilot. This kind of servo valve is difficult in manufacture and maintenance due to its complicated mechanical structure. Besides, using a small electric signal to control a very heavy load or a small movement of the flapper to cause a large distance movement of the controlled object, its transfer function is too high to keep a stable and accurate control.
The said disadvantages of the motor-operated machine or hydraulic machine are the ones to be obviated by the present invention.
In another respect, in many machines such as drilling machine the drill must be quickly approached to the object to be drilled for saving time (Rapid Approach); and then drill with a certain steady speed (Feed); and then drill with a relatively low speed when the drilling is almost completed (Fine Feed); and return with a high speed in order to save time (Rapid Return). And this operation continues reciprocatically. In other words, the knife move to and fro for a cycle and can be deemed as a reciprocating motion of a controlled object between two positions.
The automatic reciprocating motion may be divided into several types. (1) Constant speed type: The moving rate keeps constant from the starting position to the end position. (2) End deceleration type: the moving object decelerates at the end position for preventing shock and also for changing moving direction easily. (3) Variation speed type: The speed of the moving object may be adjusted at each points on to and fro path for the purpose of requirement (necessary). (4) Rapid return type: to return quickly from end point to starting point such as the said drilling machine.
The conventional machines actuated by constant speed motor or hydraulic machine using mechanical mechanisms such as cams for changing the moving speed during the reciprocating motion. If different type of speed is required for a moving object during the reciprocating motion different mechanical mechanism is to be manufactured the design for the mechanical mechanisms must be so complicated that cause noisy and damages. Further, the power transmission in said mechanical mechanisms depends on the point or line contact transmission thus the output power is limited.